This invention relates to a data input device and, more particularly, to a data Input Device well suited for use as a manual data input device (MDI) in a numerical control apparatus.
Various electronic devices such as electronic cash registers generally have keyboard means comprising a number of keys which are depressed to input the desired data. The keyboard includes keys for entering letters of the alphabet to identify the category of the input data, for entering numerical values, and for entering a variety of symbols such as period and asterisk symbols. Each key is divided into upper and lower stages, with either a numerical value or symbol being assigned to the upper stage and a letter of the alphabet being assigned to the lower stage. Separately provided is a shift key that is depressed to select the upper stage and then released to restore the lower stage. If the upper stage has been selected, depressing one of the keys will enter the numerical value or the symbol assigned to the upper stage of that key. Depressing the same key will, however, enter the letter of the alphabet assigned to the lower stage of the key if the lower stage has been selected by the shift key.
The provision of the shift key thus enables more than one item of information to be entered by a single key. For example, as described above, one key can enter a letter of the alphabet and either a numerical value or a symbol. This permits a reduction in the number of keys and in the size and cost of the apparatus.
Various machine tools and robots now come equipped with numerical control devices that incorporate a manual data input device (MDI). Operating the keyboard of the MDI allows one to enter the numerical control data manually and to correct, delete from and add to the machining data stored in the memory of the numerical control device. Keys of the data input keyboard provided on the MDI are, like the cash register described above, divided into an upper stage for a numerical value or for a symbol and a lower stage for a letter of the alphabet. A separate shift key is employed to select the upper stage or lower stage. Depressing one of the above-mentioned keys following the selection of the upper stage allows the operator to enter the numerical value or the symbol assigned to the upper stage of that key, whereas depressing the key following the selection of the lower stage permits the operator to enter the letter of the alphabet assigned to the lower stage of that key. Thus the advantages offered are the same as those described in connection with the cash register.
With the keyboard devices of the type described, however, an operator unfamiliar with the key-in operation may forget to use the shift key or may not operate it correctly. The result would be an input of incorrect data and a concomitant reduction in the data input speed arising from the need to correct the input errors.